There are numerous shapes, styles and constructions of absorbent articles designed to absorb and retain menstrual fluid or urine, the latter being used to alleviate urinary incontinence. These pads are generally placed against the perineal area of a subject and are held in place by the crotch portion of an undergarment. However, certain products have an integral panty, while others use straps or belts as affixing devices. Finally, certain absorbent products cover a larger area, e.g., infant and adult incontinent diapers. Thus, for purposes of the present invention, terms such as absorbent article or pad are meant to encompass all of these types of devices.
The use of a composite structure comprised of cellulosic fibers and superabsorbent powder as an absorbent for diapers, catamenial pads, incontinence pads, and other absorbent articles is well known. One problem associated with the application of this composite is its limited liquid transport capacity, caused by the so called "gel block" phenomena. When liquid is initially absorbed the superabsorbent swells and forms a gel, however, this gel inhibits further liquid absorption within the absorbent structure. This problem is particularly severe after long wearing with a thin layer construction that has a very small cross section or critical mass for wicking to take place after liquid is introduced.
Prior attempts have been made to reduce or eliminate the gel-block phenomenon, For example, U.S. Pat. No. 4,798,603 claims an absorbent article with a liquid-permeable transport layer placed between the cover and the absorbent core. The transport layer is made of a material which is less hydrophilic than the absorbent core and which has an effective average pore size that is smaller than the cover layer pore size. U.S. Pat. No. 4,892,532 discloses an absorbent article with a thin spun-bonded hydrophobic cover and a hydrophobic melt-bonded fabric layer between the cover and the absorbent core. The hydrophobic melt-bonded layer has a higher basis weight than the cover fabric. U.S. Pat. No. 4,908,026 discloses an absorbent article with a cover that has perforations arranged in the center of the product. A "flow zone control" layer is placed between the cover and the absorbent core in the area under the cover's perforations. U.S. Pat. No. 5,037,409 discloses an absorbent article with a "flow-modulating" layer between the absorbent and the cover. This flow-modulating layer consists essentially of hydrophilic meltblown fibers. U.S. Pat. No. 4,578,070 discloses an absorbent product with a first layer of synthetic resilient fibers united to a second layer with a higher capillary pressure than the first layer. The difference in capillary pressure causes fluid to be preferentially drawn into the second layer. The united layers are corrugated to form a stable structure.
None of these transfer layers, nor any combination of absorbent structures known in the prior art is fully effective against gel blocking. Moreover, many of the proposed solutions add unduly complex combinations of materials and/or structural features to the absorbent product making them less efficient to manufacture and more expensive. It therefore would be desirable to provide an absorbent structure that eliminated gel blocking. Accordingly, it is an object of the present invention to provide an absorbent article that comprises a modified absorbent core that channels fluid toward unwetted portions of absorbent material.
Additionally, it has been found that certain absorbent products tend to exude absorbed fluids when pressed between the legs of the wearer. Although attempts have been made to create absorbent materials that retain absorbed fluid under pressure, much of the exudate flows from the peripheral edge of the pad. It is therefore a further object of the present invention to provide absorbent articles that reduce or eliminate leakage along their edges.
Along with the above-described improvements in materials and articles for absorbing body fluids and efficiently distributing them within absorbent articles, the overall geometry of absorbent structures has been constantly refined. The shape of an absorbent article has two important aspects. First, shape largely dictates the comfort with which an absorbent article may be worn. Secondly, shape also contributes to absorbent performance by enabling the absorbent materials to remain in contact with the body or otherwise disposed in an appropriate position. For these reasons, it is desirable to eliminate phenomena such as twisting or "roping," folding along non-conformal axes, crushing, sliding, and other movement that detracts from absorbency, causes discomfort or causes the exudation of absorbed fluid. It is therefore an object of the present invention to provide improvements in the geometry of absorbent products. In particular it is an object of this invention to provide pads that will exhibit improved conformance with the perineal region of a wearer when used as either a catamenial pad or female urinary incontinence appliance.